Refresh light uniforms only when needed

After this change, if 'clean' property is added to an uniform and
evaluates to true, the uniform is not uploaded to the GPU. This is used
to avoid needlessly refreshing lights uniforms when the material changes
but the program does not, saving CPU usage.

src/renderers/WebGLRenderer.js

@@ -4287,6 +4287,7 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 		var refreshProgram = false;
 		var refreshMaterial = false;
+		var refreshLights = false;
 
 		var program = material.program,
 			p_uniforms = program.uniforms,
@@ -4299,12 +4300,15 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 			refreshProgram = true;
 			refreshMaterial = true;
+			refreshLights = true;
 
 		}
 
 		if ( material.id !== _currentMaterialId ) {
 
+			refreshLights = ( refreshLights || _currentMaterialId === - 1 );
 			_currentMaterialId = material.id;
+
 			refreshMaterial = true;
 
 		}
@@ -4408,14 +4412,20 @@ THREE.WebGLRenderer = function ( parameters ) {
 				 material instanceof THREE.MeshLambertMaterial ||
 				 material.lights ) {
 
+				refreshLights = ( refreshLights || _lightsNeedUpdate );
+
 				if ( _lightsNeedUpdate ) {
 
-					setupLights( program, lights );
+					setupLights( lights );
 					_lightsNeedUpdate = false;
-
 				}
 
-				refreshUniformsLights( m_uniforms, _lights );
+				if ( refreshLights ) {
+					refreshUniformsLights( m_uniforms, _lights );
+					markUniformsLightsClean( m_uniforms, false );
+				} else {
+					markUniformsLightsClean( m_uniforms, true );
+				}
 
 			}
 
@@ -4696,6 +4706,32 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 	};
 
+	// If uniforms are marked as clean, they don't need to be loaded to the GPU.
+
+	function markUniformsLightsClean ( uniforms, clean ) {
+
+		uniforms.ambientLightColor.clean = clean;
+
+		uniforms.directionalLightColor.clean = clean;
+		uniforms.directionalLightDirection.clean = clean;
+
+		uniforms.pointLightColor.clean = clean;
+		uniforms.pointLightPosition.clean = clean;
+		uniforms.pointLightDistance.clean = clean;
+
+		uniforms.spotLightColor.clean = clean;
+		uniforms.spotLightPosition.clean = clean;
+		uniforms.spotLightDistance.clean = clean;
+		uniforms.spotLightDirection.clean = clean;
+		uniforms.spotLightAngleCos.clean = clean;
+		uniforms.spotLightExponent.clean = clean;
+
+		uniforms.hemisphereLightSkyColor.clean = clean;
+		uniforms.hemisphereLightGroundColor.clean = clean;
+		uniforms.hemisphereLightDirection.clean = clean;
+
+	};
+
 	function refreshUniformsShadow ( uniforms, lights ) {
 
 		if ( uniforms.shadowMatrix ) {
@@ -4770,6 +4806,8 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 			var uniform = uniforms[ j ][ 0 ];
 
+			if ( uniform.clean ) continue;
+
 			var type = uniform.type;
 			var value = uniform.value;
 
@@ -4999,7 +5037,7 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 	};
 
-	function setupLights ( program, lights ) {
+	function setupLights ( lights ) {
 
 		var l, ll, light, n,
 		r = 0, g = 0, b = 0,